Manufacture of high wet strength paper



United States Patent MANUFACTURE OF HIGH WET STRENGTH PAPER William F.Fowler, Jr., Donald R. Spear, and Lee K. Tong,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y.,a corporation of New Jersey No Drawing. Application February 14, 1951,Serial No. 210,986

s Claims. c1. 92-4 This application relates to the manufacture of a highwet strength sized paper obtained by beater sizing the pulp from whichthe paper is obtained with a polyalkyl acrylate and a wax dispersion.

Ordinarily, paper is sized to resist the penetration of liquids thereinand to give the paper a certain amount of body. Also for many purposesit is desirable that the paper have a substantial wet strength,particularly where the paper is to come in contact with water or aqueoussolutions of various types. The sizing of paper at the present time inmany cases involves the precipitation in the pulp in a dispersedcondition of stearic acid (or its aluminum salts) from a solution ofsodium stearate by the addition of aluminum sulfate or the like thereto.Recently aluminum chloride has been suggested for this purpose.

To impart high wet strength to paper, the addition to the pulpdispersion of water soluble urea-formaldehyde resins ormelamine-formaldehyde resins after the Jordaning operation, but prior toits dispersing on the wire of the paper machine, has been suggested.Although this method of preparing high wet strength paper has been foundto be satisfactory in some instances, in other instances the presence ofthe formaldehyde resins has been considered objectionable, particularlywhere the prevalence of even a trace of formaldehyde cannot betolerated. Also, the preparation of sized high wet strength papers inthis fashion has involved several operations and a large quantity ofexpensive equipment.

Other methods of increasing the wet strength of paper have beenproposed. For instance, latices of various types have been suggested asbeing suitable for this purpose. Many of these materials have been foundto be unstable in the presence of ultraviolet light and also some ofthese materials contain sulfur, which is undesirable in some cases.Hydrosols of polyvinyl acetate have been suggested both as coatingcompositions for paper and for use in paper tub sizing operations. Thisresin, however, is not sufiiciently hydrophobic to be useful as a sizingagent.

One object of our invention is to provide a method for use in thepreparation of paper which simultaneously sizes the paper and increasesits wet strength. Another object of our invention is to prepare a highwet strength paper, the dry strength of which is commensurate with thatordinarily obtainedin paper manufacture. A further object of ourinvention is to provide a method of preparing high wet strength sizedpaper in which polyalkyl acrylate resins are employed in the pulp fromwhich the paper is prepared.

We have found that by adding to a paper pulp while in suspension apolyalkyl acrylate and a wax dispersion, together with an acidiccompound of aluminum, that the resulting paper obtained therefrom hasboth high wet. strength and sized characteristics. We have found,however, that in order to obtain such a paper it is necessary to firstprovide the cellulose fibers with surfaces to ice which both thepolyalkyl acrylate and the wax dispersion will adhere.

The material which is added to the pulp suspension to render thecellulose fibers adherent of the sizing material is known as a sizingaid and may be either gelatin, the water soluble salt of l-pimaricacid-maleic anhydride adduct, or the water soluble salts of abietic acidor of hydrogenated abietic acid. This sizing aid in aqueous solution isadded to the pulp suspension preliminary to the addition of the sizingmaterial as referred to herein.

One method of preparing the water soluble salt of 1- pimaric acid-maleicanhydride adduct which may be either an alkali metal salt, an ammoniumsalt, or an amine salt, is as follows, illustrating the preparation ofthe sodium salt: 98 parts of sodium hydroxide pellets were dissolved in1000 parts of distilled water and the solution was heated on a steambath with stirring. When the temperature of the solution was about C.,325 parts of l-pimaric acid-maleic anhydride adduct which had beenpreviously ground to a fine powder were added. Almost immediate solutionoccurred to produce a dark brown fluid containing 30.2 per cent ofsolids. This solution was cooled to room temperature, and diluted to thedesired concentration and employed for addition to a pulp suspension.The l-pimaric acid-maleic anhydride adduct is conveniently prepared byheating together l-pimaric acid and maleic anhydride. A glassy productis obtained thereby, which is ground to a fine powder and used in thatform.

If the ammonium salt of the adduct is desired, it may be prepared asfollows: 302 parts of commercial grade abietic acid were ground to afine powder and slowly heated to 210 C. with 98 parts ofnialeicanhydride. When the temperature had reached 100 C., the massmelted. At 160 C. it began to darken slightly, but the temperature wasslowly raised to 210 C. over the period of an hour. After cooling, 100parts of the finely divided product was added to a mixture of 300 partsof distilled water and 54 parts of 28 per cent aqueous ammoniumhydroxide. The resulting clear brown solution was heated briefly withstirring on the steam bath and was diluted with distilled water to asolution having a solids content of 5 per cent.

After the sizing aid has been added to the pulp suspension, there isthen added thereto a polyalkyl acrylate resin in the form of itshydrosol, an aqueous dispersion of wax in water and an acid form ofaluminum.

The polyalkyl acrylate hydrosol may be prepared as follows: 0.0125 partof potassium per-sulfate and 1.25 parts of sodium lauryl sulfate weredissolved in 500 parts of distilled water and heated with stirring on asteam bath in a vessel equipped with a reflux condenser, stirrer, anddropping funnel. When the solution had become hot, parts of freshlydistilled methyl acrylate was added dropwise with stirring. Thepolymerization was complete in about 45 minutes. The resultant hydrosolwas used in the examples described herein.

The wax dispersion, as employed in accordance with our invention, may beprepared by incorporating a dispersing agent such as glycerolmonostearate or some wetting agent in water, and heating the mass on thesteam bath to a temperature approaching the boiling point of water. Waxis then added While maintaining the high temperature and the mass issteamed. The elevated temperature melts the wax and it becomes uniformlydispersed in the water. Upon cooling, an aqueous wax dispersion isobtained suitable for use in accordance with our invention. Althoughparafiin wax has proved to be satisfactory, and because of its pricewould preferably be employed in actual operations, nevertheless if it isdesired, other waxes may be employed, such as beeswax, carnauba wax, orspermaceti, in preparing the wax dispersion referred to.

The acidic aluminum salt which may be employed is any water soluble saltof aluminum with a strong acid. Aluminum sulfate or aluminum chlorideordinarily comes into use in this connection and either of these saltsis suitable for the purpose at hand.

In ordinary operations, our invention is carried out by first subjectingthe aqueous slurry of pulp in the beater to a beating operation toobtain the desired slownesspreferably a slowness of -50 seconds(Williams). Excessive beating reduces the sizing values and wet strengthof the paper prepared therefrom. There is then added the sizing aid,followed by the addition of the hydrosol of the polyalkyl acrylate, thewax dispersion, and the aluminum salt. For best results the aluminumsalt should not be contacted with either the resin or the wax dispersionalone, the aluminum salt being the agent which promotes the properreaction in the pulp suspension. Therefore, for convenience inoperation, it is desirable that the aluminum salt be added last.

In preparing the hydrosol of the polyalkyl acrylates, we have found thatthe surface-active agent which is employed in that preparation should beof anionic type and that it should be not more than 2 per cent andpreferably 1 per cent or less (but at least 0.1%) based on the monomercontent of the mass. Some surfaceactive agents which may be employed aresodium higher alcohol sulfates, sodium salts of higher fatty acids,sulfated fatty alcohols, and the like. The alkyl acrylates employed maybe either tthe lower alkyl acrylates of 'simple acrylic acid such asmethyl acrylate or ethyl acrylate or the lower alkyl esters of themethacrylic acids such as methyl methacrylate or ethyl methacrylate.

In carrying out our invention, it is desirable to use an amount ofsizing aid, i. e. gelatin or the water soluble salt of pimaricacid-maleic anhydride adduct, abietic acid,

or hydrogenated abietic acid, in the proportion of approximately0.l5-l.5%, based on the dry weight of the cellulose pulp which wasemployed in preparing the paper. The polyalkyl acrylate should beemployed to impart the desired properties in an amount such that theproportion thereof is .75-%, based on the dry weight of the pulpemployed in making the paper. The wax employed should be in theproportion of .75-7.5%,

- based on the dry weight of the pulp employed in preparing the paper.The aluminum salt of a strong mineral acid which is employed should beadded in the proportion of 1-10% based on the dry weight of the pulpwhich is employed in making the paper.

The following examples illustrate our invention:

Example 1.To 3,000 parts of a 2% per cent aqueous slurry of an alphacellulose pulp beaten to a Williams slowness of 25 seconds was added thefollowing materials in the order listed:

" parts of a 14 percent aqueous solution of aluminum chloride.

1 The pulp was then diluted and sheets were formed in 'a Noble and Woodhand sheet device.

paper was dried for three minutes at 200210 F. on a The resulting rotarydrum dryer.

The sheets were tested and the following values were found:

Wet strength, 7% Cobb size, 0.168

Valley penetration, 24.

The wet strength of the sheets was determined by immersing the sheet fortwo hours in distilled water at room temperature and then measuring thebursting strength on the Minden paper tester in p. s. i.

The Cobb size test is recorded in grams increase in weight, and wasmeasured according to TAPPI standard No. T441 m 45.

The Valley penetration recorded in seconds was meas ured as follows: A2-inch square sample of paper was mounted between two Wooden blocks thathad been drilled to allow an electrolyte (516 ml. distilled water, 1

24 grams of NaCl, 60 ml. glycerine) to contact both sides of the papersimultaneously over a circular area of approximately 1 inch diameter. Apotential is applied that allows 200 m. a. of current to flow when nopaper sample is present. When a paper sample is mounted in the blocks,the time in seconds is noted from the moment the electrolyte is firstbrought in contact with the paper sample until m. a. of current flowsthrough the paper sample.

Example 2.The procedure of Example 1 was followed exactly except that 50parts instead of 20 parts of the paraflin wax dispersion was used. Upontesting, the results obtained were as follows:

Wet strength, 5 /2 Cobb size, 0.117 Valley penetration, 55.

Example 3.3,000 parts of 2% percent pulp suspension was beaten to aslowness of 20-25 seconds and there was then added thereto the followingmaterials in the order listed:

The pulp was diluted, sheets were formed therefrom, and the paper wasdried as in Example 1. The sheets were tested and gave the followingvalues:

Wet strength, 7 /2 Cobb size, 0.179 Valley penetration, 26.

Example 4.--3,000 parts of a 2%. percent aqueous slurry of pulp wasbeaten to a Williams slowness of 20-25 seconds and the followingmaterials in the order listed were added:

5 parts of an aqueous solution containing 4.4 per cent of gelatin, 0.12per cent of formaldehyde, and 0.007 per cent of chromic chloride decahydrate 20 parts of the hydrosol polyethyl acrylate such as described inthe preceding example 20 parts of a 10 per cent aqueous dispersion ofparaffin wax 25 parts of a 14 per cent solution of aluminum chloride inwater.

The results obtained were as follows:

Wet strength, 7% Cobb size, 0.181 Valley penetration, 22.

We have found that without the use of the combination of the waxdispersion and the polyalkyl acrylate, both high wet strength andresistance to penetration by water are not obtained. Also, the additionof the sizing aid is necessary to assure adherence of the sizingmaterial to the collulose fibers, while the presence of the aluminumsalt is necessary to assure satisfactory sizing operations.

The paper to which high wet strength is imparted by our invention may beany type of paper-making pulp, such as sulfite pulp, kraft pulp, or anyother type of pulp which is employed in making paper. We have found thatour invention is eminently suitable for use in preparing paper fromkraft pulp, both of the bleached and non-bleached type. However, withnon-bleached kraft pulp, wet strength and sizing values are obtainedwhich appear to be superior to those of any papers which have beenprepared heretofore to our knowledge.

We claim:

1. A high wet strength paper containing therein, based on the dry weightof the pulp employed in its preparation, the following in theproportions given:

Per Cent A sizing aid selected from the group consisting of gelatin,water soluble salt of pimaric acidmaleic anhydride adduct, the watersoluble salt of abietic acid, and the water soluble salt of hydrogenatedabietic acid 0.l-l.5 Polyalkyl acrylate, the alkyl being of not morethan two carbon atoms .75- Wax .75-7.5 Aluminum salt selected from thegroup consisting of aluminum sulfate and aluminum chloride 1-10 2. Ahigh wet strength paper containing therein, based on the dry weight ofthe pulp employed in its preparation, the following in the proportionsgiven:

Per Cent Gelatin 0.151.5 Polyalkyl acrylate, the alkyl being of not morethan two carbon atoms .75-15 Wax .757.5 Aluminum salt selected from thegroup consisting of aluminum sulfate and aluminum chloride 1-10 3. Ahigh wet strength paper containing therein, based on the dry weight ofthe pulp employed in its preparation. the following in the proportionsgiven:

Per Cent A water soluble salt of pimaric acid-maleic anhydride adduet0.151.5 Polyalkyl acrylate, the alkyl being of not more than two carbonatoms .75-15 Wax .757.5 Aluminum salt selected from the group consistingof aluminum sulfate and aluminum chloride 1-10 4. A high wet strengthpaper containing therein, based on the dry weight of the pulp employedin its preparation, the following in the proportions given:

Per Cent Gelatin 0.151.5

Per Cent Polymethyl acrylate .75-15 Wax .75-7.5 Aluminum salt selectedfrom the group consisting of aluminum sulfate and aluminum chloride 1-105. A high wet strength paper containing therein, based on the dry weightof the pulp employed in its preparation, the following in theproportions given:

Per Cent A Water soluble salt of pimaric acid-maleic anhydride adduct0.15-1.5 Polymethyl acrylate .75-15 Wax .757.5

Aluminum salt selected from the group consisting of aluminum sulfate andaluminum chloride l-l0 6. A method of preparing high wet strength paperwhich comprises incorporating into a suspension of paper pulp a sizingaid selected from the group consisting of gelatin, the water solublesalt of pimaric acid-maleic anhydride adduct, the water soluble salt ofabietic acid, and the water soluble salt of hydrogenated abietic acid,and then adding thereto a polyalkyl acrylate hydrosol, a wax dispersion,and an aluminum salt selected from the group consisting of aluminumsulfate and aluminum chloride, and then forming paper therefrom.

7. A method of preparing high wet strength paper which comprisesincorporating into a suspension of paper pulp a solution of a sodiumsalt of pimaric acid-maleic anhydride adduct, then adding thereto apolyalkyl acrylate hydrosol, an aqueous dispersion of wax, and analuminum salt selected from the group consisting of aluminum sulfate andaluminum chloride, and then converting the pulp into paper.

8. A method of preparing high wet strength paper which comprisesincorporating into a suspension of paper pulp an aqueous solution ofgelatin, then adding thereto a hydrosol of polymethyl acrylate, adispersion of paraffin wax in water, and an aqueous solution of aluminumchloride, and then forming the pulp into paper.

References Cited in the file of this patent UNITED STATES PATENTS1,706,841 Clapp Mar. 26, 1929 1,942,438 Manson Jan. 9, 1934 2,021,172Buoy Nov. 19, 1935 2,119,509 Barnhart June 7, 1938 2,315,675 TrommsdorfApr. 6, 1943 2,325,302 Britt July 27, 1943 2,343,065 Kumler Feb. 29,1944 2,343,090 Smith Feb. 29, 1944 2,354,574 Carson July 25, 19442,539,183 Child Jan. 23, 1951

1. A HIGH WET STRENGTH PAPER CONTAINING THEREIN, BASED ON THE DRY WEIGHTOF THE PULP EMPOLYED IN ITS PREPARTION, THE FOLLOWING IN THE PROPORTIONSGIEN: